Vote 1 CA18DET........

Seriously though - How fast do you want to go?

1200 + CA18DET with a T28 (SR20) ball bearing turbo & some RB25 injectors & you're looking at 11's.
Which (I reckon) is just about as much power as you want on the road.

If you're off to the track, you're gonna have all sorts of fun getting the power to the ground even in stock CA trim.
I mean the A15's give the CA guys plenty to think about at the track due to usable power.
So it's a case of bigger isn't necessarily better for the track.

Beyond that - bigger turbo, forgies etc, etc..... $$$$$$$$$!!

If you want faster again, then you're probably looking at a drag-specific car anyway.
In which case you may as well go down the SR20DET path as you don't have to worry about rego etc.

ie/ My two cents = SR20DET for the strip, CA18DET for street .